The more the additional functions increases, the more concentration of every manufacturer is directed to the limited space as to make the outmost efficiency to accommodate the operating keys corresponding to the additional functions.
For instance, a traditional compact keyboard can be coupled to a PDA-phone (Personal Digital Assistant) in order to facilitate the user to compile or edit a text document. The key on such compact keyboard is too small in dimension and may lead the user to inconvenience during pressing of the keys, hence preventing fast data input. Most PDA-phones are equipped with hand written input devices consisting of a touch screen and a stylus for tapping input data and writing words or characters, thereby quickening the data input.
Another type of mobile phone is available in the market, wherein the mobile phone is equipped with an externally connected keyboard such that when the user requires additional keys for the added functions, the object can be achieved by attachment of the keyboard to the PDA. USB devices, wireless connection devices (like Bluetooth-enabled devices) can be implemented for coupling the keyboard to the PDA. The attachment of keyboard to the PDA in order to obtain the expanded keys though does not result in high cost, but decrease the portability of the mobile phone when considered from the user's views.
Therefore, under the consideration to provide multi-functions for the mobile phone and simultaneously for minimizing its volume, it is an important factor for the manufacturers concerned to provide an easy data input mode of the mobile phone.